Method and apparatus for generating pseudo random numbers in a video device having an embedded cipher unit

Abstract

A video source device includes a cipher unit. The video source device uses the cipher unit to generate cipher bits for ciphering video to be transmitted to protect the video from unauthorized copying. The video source device authenticates video receiving devices using a symmetric ciphering/deciphering process that requires the video source device to generate and provide the video receiving device with a pseudo random number as the seed/basis number for the symmetric ciphering/deciphering process. The video source device is further provided with a state machine that controls the cipher unit to generate the required pseudo random number for the video source devices, thereby eliminating the need of having to provide separate circuitry to generate the required pseudo random numbers.

1. A pseudo random number generator comprising:
 a cipher unit to generate a sequence of ciphering bits to cipher a stream of data including at least video data; and 
 a state machine coupled to the cipher unit to also use the ciphering unit to generate a plurality of pseudo random numbers based on selected ones of said cipher bits wherein the state machine is equipped to transition to a continuous clocking state that includes, upon power on or reset, causing the cipher unit to be continuously clocked to introduce entropy into the cipher unit, 
 wherein the state machine operates in one of four states: a continuous clocking state (E 0 ), a first cipher bit taking state (E 1 ), an output state (E 2 ), a second cipher bit taking state (E 3 ), and an active state (also referred to as the authenticated state), 
 and during operating the state machine enters state E 0  upon power on and while in state E 0 , the state machine causes the cipher unit to be continuously clocked to incorporate entropy into the cipher unit, 
 from state E 0 , the state machine transitions to state E 1 , first cipher bit taking state, upon receipt of a request for a first pseudo random number, after clocking the cipher units for n clocks, where n is an integer, in state E 1 , the state machine causes a number of output ciphering bits of the cipher unit to be taken and stored into a temporary storage location for output, 
 from state E 1 , the state machine enters state E 2 , upon storing the taken ciphering bits, in state E 1 , the state machine causes the stored ciphering bits to be output as the requested pseudo random number, 
 in state E 3 , the state machine causes a number of the output ciphering bits of the cipher unit to be taken and stored into a temporary storage location for output, 
 in the active state, the cipher unit is used to generate ciphering bits to cipher the video before transmitting to a video receiving device and the cipher unit is not available for pseudo random number generation, 
 from the active state, the state machine transitions back to E 0 , the continuous clocking state, if the authentication unit is notified of the video receiving device becoming unauthorized of becoming detached from the video source device. 
 
   
   
     2. The pseudo random generator of  claim 1 , wherein the state machine is equipped to transition from said continuous clocking state to said first cipher bit taking state, in response to a subsequent request after n clocks for said first pseudo random number, where n is an integer, and to transition from said first cipher bit taking state to said output state, upon storing the first output cipher bits. 
   
   
     3. The pseudo random generator of  claim 1 , wherein the state machine is equipped to transition from said output state to a selected one of the continuously clocking state, the second cipher bit taking state, and the authenticated state depending on whether upon provision of the first pseudo random number, an indication of an unsuccessful authentication using the first pseudo random number, another request for a second pseudo random number, or an indication of a successful authentication using the first pseudo random number is received. 
   
   
     4. The pseudo random generator of  claim 1 , wherein the state machine is equipped to transition from said second cipher bit taking state to said output state upon taking the second plurality of output cipher bits of the cipher unit and storing the second output cipher bits. 
   
   
     5. The pseudo random number generator of  claim 1 , wherein the state machine is further equipped to transition from said authenticated state to said second cipher bit taking state upon receiving another request for a third pseudo random number, and to said continuously clocking state upon receiving a selected one of an unauthenticated notification and a detachment notification.